Developer apparatus

ABSTRACT

Apparatus is described for developing a latent image on a sheet. Toner is deposited on the sheet by passing the sheet over a projecting portion of a cylindrical roller in contact with a film of fluid established by rotating the roller. The fluid has toner entrained therein and is supplied to the roller by a pump via a space between the roller and a shroud, which surrounds the roller except for an opening through which the projecting portion of the roller extends. Wiper means both remove residual material from the roller and prevent the removed material from returning to said space.

United States Patent [72] Inventors Louis A. SmiIZer; 2,590,538 3/1952 Huck... 1 18/602UX Byung Sik l-long, San Diego. Calif. 2,861,541 1 1/1958 Hornbostel 1 18/104UX [211 App]. No. 746,839 2,875,094 2/ 1959 Bloem et a1 1 18/602X [22] Filed July 23, 1968 2,995,469 8/1961 LeClaire. .v 1 l8/103X [45] Patented Feb. 9, 1971 3,242,902 3/1966 Ulary I 18/602X [73] Assignee Stromberg Datagraphix, Inc. 3,245,341 4/ 1966 Childress et a1 1 18/637X a corporation of Delawar 3,367,791 2/1968 Lein .11 8/637( LX )UX 3,368,526 2/1968 Matsumoto et al. 1 18/637 [54] DEVELOPER APPARATUS 10 Claims, 2 Drawing Figs.

Primary Examiner-Morris Kaplan Attorney-Anderson, Luedeka, Fitch, Even & Tabin ABSTRACT: Apparatus is described for developing a latent image on a sheet. Toner is deposited on the sheet by passing the sheet over a projecting portion ofa cylindrical roller in contact with a film of fluid established by rotating the roller. The fluid has toner entrained therein and is supplied to the roller by a pump via a space between the roller and a shroud, which surrounds the roller except for an opening through which the projecting portion of the roller extends. Wiper means both remove residual material from the roller and prevent the removed material from returning to said space.

PATENTED FEB 919m //////////////2 INVENTORS LOUIS A.$MITZER BY avuucs sm nous 'ATYORNEVS 1 DEVELOPER APPARATUS This invention relates to developer apparatus and, more particularly, to improved apparatus for developing a latent image on a sheet.

Some forms of reproducing apparatus employ developer apparatus to automatically develop the latent image on'a sheet which has been exposed to a particular object to be copied, such as a printed sheet or microfilm. One example is in the art of electrostatic printing in which developer apparatus is used to develop a latent electrostatic image on a sheet. More particularly, the sheet, which a has a photoresistive surface such as a coating of zinc oxide, is charged uniformly in a darkened environment to an electrostatic potential of, for example, several hundred volts. The light image to be printed is projected onto the charged surface, discharging portions of the surface to thereby produce a latent electrostatic image. The developer apparatus develops the latent electrostatic image by depositing a finely divided marking material, known as toner, on either the charged or the uncharged areas of the sheet, but not both. The toner is then fixed by heating it to an appropriate temperature or by the removal of solvent therefrom, or by other known methods.

Several techniques are known for applying toner to latent image bearing sheets so that toner will adhere to the sheet in desired areas. One technique is by cascading the toner in dry form over the surface of the sheet, and removing the excess toner either by allowing it to slide off the sheet by the force of gravity, or by blowing the excess toner off with a fan. Another technique utilized by prior art developer apparatus is to entrain the toner particles in a finely divided magnetic powder and to utilize a magnetic brush for distributing the toner and magnetic powder over the surface of the sheet. A third technique for distributing the toner is to entrain the toner in a dielectric liquid which is then brought in contact with the surface bearing the latent image. The developer apparatus of the present invention utilizes the latter technique.

A significant problem encountered in developer apparatus utilizing liquid entrained toner is that repeated developments may cause a deterioration of image quality due to a depletion of toner particles in the liquid. This may occur even after a very short period of use, since the concentration of toner in the liquid near where the liquid is brought into contact with the sheets may lower very rapidly.

in utilizing liquid entrained toner in developer apparatus, it is desirable to pass the image bearing sheet through some type of means for removing excess liquid therefrom. This is often done by passing the wet sheet through a pair of squeeze rollers which provides sufficient pressure to squeeze the excess liquid from the sheet. With long use, such squeeze rollers may become coated with heavy deposits of toner, causing soiling of the sheets. Even if the rollers are cleaned periodically, the squeeze rollers may produce ghost images of prior sheets on later sheets, due to the transfer of toner accumulated on the rollers from previous sheets, to the later sheets.

It is known that images of greater density and greater uniformity across large toned areas can be produced by providing a conductive intensifier electrode" adjacent and generally parallel to the surface of the latent image. A problem encountered with some intensifier electrodes is that repeated use may cause accumulations of caked toner particles and other undesirable residues on the intensifier electrodes. These accumulations adversely affect the uniformity of image development by altering the spacing between the electrode and the latent image, and often are sufficiently tacky to adhere to the image bearing sheets passed thereover, resulting in buckling of image sheets and jamming of the sheet transporting mechanism.

It is an object of the present invention to provide improved apparatus for developing a latent image on a sheet.

Another object of the invention is to provide developer apparatus which produces images of consistent quality over a relatively large number of successive sheets.

Another object of the invention is to provide electrostatic developer apparatus capable of reproducing solid black areas with high quality and in which buckling or soiling of sheets is avoided.

A further object of the invention is to provide developer apparatus utilizing squeeze rollers for removing a toner-entraining developer liquid from developed sheets and in which the rollers do not become coated with heavy deposits of toner, nor do they produce ghost images of prior sheets on later sheets.

It is another object of the invention to provide developer apparatus in which the need for periodic manual cleaning is minimized.

Other objects of the invention will become apparent to those skilled in the art from the following description, taken in connection with the accompanying drawings wherein:

FIG. 1 is a schematic full-sectional view of apparatus constructed in accordance with the invention;

FIG. 2 is a side view, partially sectioned, of a portion of the apparatus of FIG. 1.

Very generally, the developer apparatus of the invention comprises a cylindrical roller II. A shroud l2 surrounds the roller and defines a space 13 between the roller and the shroud. The shroud has an opening 14 therein which permits a portion of the roller to project beyond the shroud. Means 16 provide a supply of liquid having entrained toner to the space 13. The roller is rotated to carry a film of the developer liquid over the projecting portion of the roller to contact the image bearing sheet. The liquid is collected, after it passes over the roller, by means which are outside the shroud.

Referring now more particularly to the drawings, the apparatus illustrated therein is for developing latent electrostatic images. The roller 11 has an outer cylindrical surface and is comprised of a conductive material, such as a suitable metal. The length of the roller is equal to or greater than the greatest width of the image-bearing sheets 10 to be developed. The shroud 12 is formed of a suitable material, such as plastic, and surrounds the roller 11 except for an elongated slot or opening 14 at the top of the shroud. Accordingly, the shroud defines a space 13, generally partially annular, between the shroud and the roller. The ends of the shroud are closed so that liquid may be contained within the space 13. The roller 11 is mounted on an axle 15 which is joumaled in the shroud at its ends and is driven by a motor 17 and a suitable drive mechanism 18.

A liquid developer mix, consisting of a dielectric liquid with a quantity of toner entrained or dispersed in it, is pumped through a conduit 19 into a plenum 21 which communicates with the space 13 and the fluid pumped into the plenum flows into the space 13 between the shroud and the roller 11.

An elongated felt wiper 51 contacts the roller 11 and serves to clean the surface of the roller 1 l as it rotates. The wiper 16 also closes one of the longitudinal openings of the annular space 13, so that liquid pumped into the space through the pienum 21 is forced to well up through the other longitudinal opening 52.

A sink 22 is disposed underneath both the shroud l2 and the conductive roller 11 and constitutes a means outside the shroud for collecting fluid, as will be explained. Fluid collected by the sink 22 is drained through a conduit 23. The sink may be comprised of any suitable material, such as molded plastic.

The conduit 23 empties into a reservoir or tank 24. For reasons which will be subsequently explained, the capacity or volume of the tank 24 is substantially greater than the volume within the space 13. An elongated shaft 26 is suitably journaled within the tank 24 and is provided with a driving gear 27 at one end thereof. Pinion gear 28 is enmeshed with the driving gear 27 and is driven on a counter shaft 29. The counter shaft is driven by suitable means, not illustrated, such as a chain or gear drive coupled to the motor 17. A pair of elongated agitator blades 31 and 32 are mounted on the shaft 26 and rotate'therewith when the shaft is driven through the driving gear 27. This agitates the liquid contained within the tank 24 to maintain an even distribution of toner particles in the liquid.

A pump 33 is immersed in the fluid in the tank and is driven through an impeller shaft 34 by a motor 36. The end of the conduit 19 opposite the plenum 211 is connected to the pump 33 and the pump 33 operates to continuously pump developer liquid from the tank 24 through the conduit 19 into the plenum 21.

Sheets carrying a latent image are fed into the developer apparatus by a pair of feed rollers 37 and 38, suitably driven, such as by the motor 117. After contacting the developer liquid, as will be explained, the wet sheets are passed between a pair of squeeze rollers 39 and ill in order to remove excess liquid from the sheet. The squeeze rollers 39 and 41 are disposed above the sink 22 so that liquid squeezed out by the squeeze rollers will be collected in the sink and drained through the conduit 23 back to the tank 24.

In order to clean the lower roller 41, an elongated felt wiper 4-2, mounted on a bracket 43, contacts the surface of the roller 41 as it rotates. The wiper contacts the portion of the surface of the roller which has just passed the image sheet, thus removing any deposit of toner on the roller. Toner removed by the wiper may fall back into the sink 22 and the liquid therein, to be returned to the tank 24.

The sheets utilized may be of any type suitable for retaining an electrostatic image thereon. Such sheets may be provided with a thin coating of zinc oxide and charged to a suitable potential in a darkened environment. When the sheets are then exposed to a light image, those areas of the sheet upon which light falls are discharged, whereas those areas upon which less light falls are discharged correspondingly less. Thus, a latent image is produced on the sheet.

The developer liquid consists of an insulating liquid carrier in which is dispersed a small quantity of developer particles. The particles are finely divided colored solids and serve as the ink of the printing process. It is presumed that developer or toner particles are composed of or coated with materials which are well separated in the triboelectric series from the material of the carrier liquid. Accordingly, the particles and the canier liquid assume opposite electrical charges with respect to each other while mingling in the tank 24.

In order to bring the image bearing paper into contact with the toner entraining liquid, the paper is driven by the feed rollers 37 and 38 over the top of the conductive roller 11. The top portion of the conductive roller projects through the opening M. The liquid developer is forced by pump pressure to well up within the space 13. When the roller ill is rotated, a film of developer liquid andits entrained toner is carried over the projecting portion of the roller. The flow of liquid upward through the opening 52, because of pump pressure, assists in the formation of the film. The film is brought into contact with the sheet being passed thereacross. This film is continuous and is constantly being replenished from the liquid being pumped into the region 13.

After passing over the roller llli, much of the fluid, partially depleted of the toner particles therein, falls past the shroud and into the sink 22. From the sink 22, it is returned through the conduit 23 to the tank 24. The film of liquid, captured momentarily between the top of the roller ill and the surface of the sheet bearing the electrostatic image, deposits particles of toner on certain areas of the sheet while not depositing on other areas, depending upon the charges placed on the sheet. For example, if the sheet is initially negatively charge, the areas which are light struck become relatively more positive. If a developer liquid is used in which the particles are negative, the particles deposit on the relatively more positive light struck areas, and are repelled from the relatively more negative areas not struck by light. On the other hand, if the developer liquid contains particles which become triboelectrically charged positive with respect to the carrier liquid, the opposite effect is achieved at development (i.e., the positive particles deposit on more negative areas not struck by light).

After the latent electrostatic image on the sheet is developed, the sheet is passed through the squeeze rollers 39 and M. The rollers are preferably coated with a thick layer of resilient material, such as polyurethane. The liquid removed from the sheet is collected in the sink 22 and the felt wiper 42 cleans the lower roller 41 to prevent the printing of ghost images from a previous sheet onto the face of the sheet passing through the squeeze roller. The sheet may then be processed in any other suitable manner.

In the zone of development, which is in the thin layer of liquid between the projecting portion of the roller 11 and the image bearing sheet, the electric field of the sheet is intensified by the presence of the conductive roller. The roller is grounded and makes the electric field lines extend perpendicular to the sheet and produces an intense field wherever the sheet is charged. Without such an intensifier electrode. the field is intense only at boundaries between charged and uncharged areas. Thus, a developer with an intensifier electrode is capable of reproducing solid black areas, while one without an intensifier electrode cannot reproduce the centers of such areas. Since no stationary intensifier electrode or sup porting member, which may become wetted with developer fluid, is used (the moving roller 11 constituting the only intensifier electrode utilized) the possibility of sheets sticking to wet electrodes or becoming soiled from toner accumulating on such electrodes is eliminated. Since the roller 11 is cleaned by the wiper 51, accumulations of toner or other residues on it are prevented. The surface of the roller remains uniformly cylindrical so that sheets passing thereover are uniformly spaced and unifonnly developed in the development zone.

The developer mixture applied to the image-bearing sheets 10 is always fresh in that it is thoroughly mixed and is at full strength, coming directly from the tank 24. Localized depletion of the toner liquid adjacent to the roller 1] is thereby avoided, since a rapid flow of fresh mixture continuously occurring through the developer passes a very large number of toner particles through the electric field of the image. This insures that enough toner particles will be deposited to satisfy or substantially neutralize the image charge, for full development of the latent image.

Since the roller 41 is constantly cleaned by the wiper 42 as the roller rotates, and since the wiper contacts the portion of the surface of the roller which hasjust passed the image sheet, the roller does not become coated with heavy deposits of toner with long use, nor does it track or produce ghost images of prior sheets on later sheets.

It may therefore be seen that the invention provides improved apparatus for developing a latent image on a sheet. The apparatus requires infrequent cleaning, is reliable in operation, produces high quality images, and avoids the production of soiled sheets or sheets having ghost images thereon.

Various modifications of the invention in addition to those shown and described herein will become apparent to those skilled in the art from the foregoing description and accompanying drawings. Such modifications are intended to fall within the scope of the appended claims.

We claim:

1. Developer apparatus for developing a latent image on a sheet, comprising, a cylindrical roller, a shroud surrounding said roller and defining a space between said roller and said shroud, said shroud having an opening therein permitting a portion of said roller to project beyond said shroud, means for providing a continuous supply of developer liquid to said space, means for rotating said roller to carry a film of the liquid from one side of said space over the projecting portion of said roller, means for conveying the latent image bearing sheet past the projecting portion of said roller in contact with the film of liquid, a wiper adjacent said roller on one side of said opening in said shroud for preventing partially exhausted liquid from returning to said space after passing over the projecting portion of said roller, and means outside said shroud for collecting partially exhausted liquid after it passes over the projecting portion of said roller and said wiper.

2. Developer apparatus according to claim 1 including a reservoir for the liquid, said reservoir having a capacity substantially greater than the capacity of said space, and means for circulating liquid from said collecting means to said reservoir and from said reservoir to said space.

3. Developer apparatus according to claim 2 including agitator means in said reservoir for mixing the liquid entering from said collecting means with the liquid in said reservoir.

4. Developer apparatus according to claim 1 wherein said collecting means include a pair of squeeze rollers for engaging the top and bottom, respectively, of the sheet and removing excess liquid therefrom.

5. Developer apparatus according to claim 4 wherein said collecting means include means positioned below said squeeze rollers for collecting liquid removed from the sheet.

6. Developer apparatus according to claim 4 including means for removing deposits adhering to the lower one of said pari of squeeze rollers.

7. Developer apparatus according to claim 6 wherein said deposit removing means comprise a wiper blade positioned to contact said lower squeeze roller just after the region of contact thereof with the sheet.

8. Developer apparatus according to claim 1 for developing electrostatic images wherein said roller is comprised of electrically conductive material.

9. Developer apparatus for developing a latent electrostatic image on a sheet, comprising, a cylindrical roller of electrically conductive material, means for providing a continuous supply of liquid having entrained charged toner particles to a partially confined region adjacent said roller, means for rotating said roller to carry a film of the liquid over the top of said rollers, a wiper for preventing liquid from returning to said partially confined region after passing over the top of said roller, and means for conveying the latent image bearing sheet over the top of said roller in contact with the film of liquid, said roller being at an electrical potential to constitute the only intensifier electrode utilized.

' 10. Developer apparatus according to claim 9 wherein said in the direction of movement of the sheet. 

1. Developer apparatus for developing a latent image on a sheet, comprising, a cylindrical roller, a shroud surrounding said roller and defining a space between said roller and said shroud, said shroud having an opening therein permitting a portion of said roller to project beyond said shroud, means for providing a continuous supply of developer liquid to said space, means for rotating said roller to carry a film of the liquid from one side of said space over the projecting portion of said roller, means for conveying the latent image bearing sheet past the projecting portion of said roller in contact with the film of liquid, a wiper adjacent said roller on one side of said opening in said shroud for preventing partially exhausted liquid from returning to said space after passing over the projecting portion of said roller, and means outside said shroud for collecting partially exhausted liquid after it passes over the projecting portion of said roller and said wiper.
 2. Developer apparatus according to claim 1 including a reservoir for the liquid, said reservoir having a capacity substantially greater than the capacity of said space, and means for circulating liquid from said collecting means to said reservoir and from said reservoir to said space.
 3. Developer apparatus according to claim 2 including agitator means in said reservoir for mixing the liquid entering from said collecting means with the liquid in said reservoir.
 4. Developer apparatus according to claim 1 wherein said collecting means include a pair of squeeze rollers for engaging the top and bottom, respectively, of the sheet and removing excess liquid therefrom.
 5. Developer apparatus according to claim 4 wherein said collecting means include means positioned below said squeeze rollers for collecting liquid removed from the sheet.
 6. Developer apparatus according to claim 4 including means for removing deposits adhering to the lower one of said pari of squeeze rollers.
 7. Developer apparatus according to claim 6 wherein said deposit removing means comprise a wiper blade positioned to contact said lower squeeze roller just after the region of contact thereof with the sheet.
 8. Developer apparatus according to claim 1 for developing electrostatic images wherein said roller is comprised of electrically conductive material.
 9. Developer apparatus for developing a latent electrostatic image on a sheet, comprising, a cylindrical roller of electrically conductive material, means for providing a continuous supply of liquid having entrained charged toner particles to a partially confined region adjacent said roller, means for rotating said roller to carry a film of thE liquid over the top of said rollers, a wiper for preventing liquid from returning to said partially confined region after passing over the top of said roller, and means for conveying the latent image bearing sheet over the top of said roller in contact with the film of liquid, said roller being at an electrical potential to constitute the only intensifier electrode utilized.
 10. Developer apparatus according to claim 9 wherein said roller is rotated in a direction to cause the top portion to move in the direction of movement of the sheet. 